Hamilton turned professional in 1987 but was unable to gain entrance to the PGA Tour. Instead he played internationally for many years, primarily on the Japan Golf Tour. When he left the Japan Golf Tour, he was the all-time leading non-Japanese money winner on it, with earnings of over 630 million yen and had won 11 times.

After eight tries, at the age of thirty eight, Hamilton went back to Qualifying School in 2003 where he finally earned his first PGA Card.